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Ultrafast Optics|69 Article(s)
Regular uniform large-area subwavelength nanogratings fabricated by the interference of two femtosecond laser beams via cylindrical lens
Kaiqiang Cao, Long Chen, Ke Cheng, Zhenrong Sun, and Tianqing Jia
Inhomogeneity and low efficiency are two important factors that hinder the wide application of laser-induced periodic surface structures. Two-beam interference is commonly used to fabricate gratings with interference periods. This study reports regular and uniform periodic ripples fabricated efficiently by the interference of two femtosecond laser beams via a cylindrical lens. The interference period is adjusted to be an integer multiple of the wavelength of a surface plasmon polariton. Regular and uniform subwavelength nanogratings (RUSNGs) on a silicon wafer of a diameter of 100 mm are fabricated with a scanning velocity of 6–9 mm/s. Bright and pure colors (including purple, blue, and red) are demonstrated on different patterns covered with RUSNGs. Inhomogeneity and low efficiency are two important factors that hinder the wide application of laser-induced periodic surface structures. Two-beam interference is commonly used to fabricate gratings with interference periods. This study reports regular and uniform periodic ripples fabricated efficiently by the interference of two femtosecond laser beams via a cylindrical lens. The interference period is adjusted to be an integer multiple of the wavelength of a surface plasmon polariton. Regular and uniform subwavelength nanogratings (RUSNGs) on a silicon wafer of a diameter of 100 mm are fabricated with a scanning velocity of 6–9 mm/s. Bright and pure colors (including purple, blue, and red) are demonstrated on different patterns covered with RUSNGs.
Chinese Optics Letters
- Publication Date: Sep. 10, 2020
- Vol. 18, Issue 9, 093201 (2020)
THz generation from water wedge excited by dual-color pulse
Min Li, Zhenyu Li, Junyi Nan, Yu Xia, Mingyang He, Feng Wang, Wenhui Lu, Shuai Yuan, and Heping Zeng
Terahertz (THz) waves could be generated through exciting a gravity-guided, free-flowing water wedge by a dual-color pulse. It is not required to rotate the optimal angle considering the water film as an ionization medium. It is demonstrated to be more effective to generate stronger THz radiation when the ionization position is on the front surface of the air water interface of the water wedge by moving its position. The effect of pulse energy on THz generation is also investigated, and it is observed that with the increase of pulse energy the THz electric field shows a quadratic rising trend. These observations are consistent with air plasma induced THz emission. Terahertz (THz) waves could be generated through exciting a gravity-guided, free-flowing water wedge by a dual-color pulse. It is not required to rotate the optimal angle considering the water film as an ionization medium. It is demonstrated to be more effective to generate stronger THz radiation when the ionization position is on the front surface of the air water interface of the water wedge by moving its position. The effect of pulse energy on THz generation is also investigated, and it is observed that with the increase of pulse energy the THz electric field shows a quadratic rising trend. These observations are consistent with air plasma induced THz emission.
Chinese Optics Letters
- Publication Date: Jul. 10, 2020
- Vol. 18, Issue 7, 073201 (2020)
Harmonically pump a femtosecond optical parametric oscillator to 1.13 GHz by a femtosecond 515 nm laser
Jiajun Song, Xianghao Meng, Zhaohua Wang, Xianzhi Wang, Wenlong Tian, Jiangfeng Zhu, Shaobo Fang, Hao Teng, and Zhiyi Wei
We demonstrate a harmonically pumped femtosecond optical parametric oscillator (OPO) laser using a frequency-doubled mode-locked Yb:KGW laser at a repetition rate of 75.5 MHz as the pump laser. Based on a bismuth borate nonlinear crystal, repetition rates up to 1.13 GHz are realized, which is 15 times that of the pump laser. The signal wavelength is tunable from 700 nm to 887 nm. The maximum power of the signal is 207 mW at the central wavelength of 750 nm and the shortest pulse duration is 117 fs at 780 nm. The beam quality (M2 factor) in the horizontal and vertical directions of the output beam are 1.077 and 1.141, respectively. We demonstrate a harmonically pumped femtosecond optical parametric oscillator (OPO) laser using a frequency-doubled mode-locked Yb:KGW laser at a repetition rate of 75.5 MHz as the pump laser. Based on a bismuth borate nonlinear crystal, repetition rates up to 1.13 GHz are realized, which is 15 times that of the pump laser. The signal wavelength is tunable from 700 nm to 887 nm. The maximum power of the signal is 207 mW at the central wavelength of 750 nm and the shortest pulse duration is 117 fs at 780 nm. The beam quality (M2 factor) in the horizontal and vertical directions of the output beam are 1.077 and 1.141, respectively.
Chinese Optics Letters
- Publication Date: Mar. 10, 2020
- Vol. 18, Issue 3, 033201 (2020)
Terahertz wave emission from water lines
Shijia Feng, Liquan Dong, Tong Wu, Yong Tan, Rui Zhang, Liangliang Zhang, Cunlin Zhang, and Yuejin Zhao
To make further understanding of terahertz (THz) wave generation from liquid water, we study THz wave emission from water lines of different diameters. The water line with a smaller diameter generates a stronger THz electric field for the diameters from 0.2 mm to 0.5 mm. The THz electric field strength and polarity change with the relative position between the incident laser and water line. Moreover, the THz energy has an optimal radiation angle of about 60°. A two-dimensional dipole array model is introduced to illustrate the phenomenon. Our observations contribute to optimizing the scheme of the liquid THz source. To make further understanding of terahertz (THz) wave generation from liquid water, we study THz wave emission from water lines of different diameters. The water line with a smaller diameter generates a stronger THz electric field for the diameters from 0.2 mm to 0.5 mm. The THz electric field strength and polarity change with the relative position between the incident laser and water line. Moreover, the THz energy has an optimal radiation angle of about 60°. A two-dimensional dipole array model is introduced to illustrate the phenomenon. Our observations contribute to optimizing the scheme of the liquid THz source.
Chinese Optics Letters
- Publication Date: Feb. 10, 2020
- Vol. 18, Issue 2, 023202 (2020)
Time-resolved study of the lasing emission from high vibrational levels of
Dongjie Zhou, Xiang Zhang, Qi Lu, Qingqing Liang, and Yi Liu
We experimentally investigated the forward 353.8 nm radiation from plasma filaments in pure nitrogen gas pumped by intense circularly polarized 800 nm femtosecond laser pulses. This emission line corresponds to the B2Σu+(v′=4)-X2Σg+(v=3) transition of nitrogen ions. In the presence of an external seeding pulse, the 353.8 nm signal was amplified by 3 orders of magnitude. Thanks to the much enhanced intensity, we performed time-resolved measurement of the amplified 353.8 nm emission based on the sum-frequency generation technique. It was revealed that the built-up time and duration of these emissions are both inversely proportional to the gas pressure, while the radiation peak power grows up nearly quadratically with pressure, indicating that the 353.8 nm radiation is of the nature of superradiance. We experimentally investigated the forward 353.8 nm radiation from plasma filaments in pure nitrogen gas pumped by intense circularly polarized 800 nm femtosecond laser pulses. This emission line corresponds to the B2Σu+(v′=4)-X2Σg+(v=3) transition of nitrogen ions. In the presence of an external seeding pulse, the 353.8 nm signal was amplified by 3 orders of magnitude. Thanks to the much enhanced intensity, we performed time-resolved measurement of the amplified 353.8 nm emission based on the sum-frequency generation technique. It was revealed that the built-up time and duration of these emissions are both inversely proportional to the gas pressure, while the radiation peak power grows up nearly quadratically with pressure, indicating that the 353.8 nm radiation is of the nature of superradiance.
Chinese Optics Letters
- Publication Date: Feb. 10, 2020
- Vol. 18, Issue 2, 023201 (2020)
High-order harmonic generation from zigzag graphene nanoribbons
Jiaqi Wu, Yinghui Zheng, Zhinan Zeng, and Ruxin Li
High-order harmonic generation originated from zigzag graphene nanoribbons (ZGNRs) induced by intense laser pulses is investigated theoretically. During the interaction between the intense mid-infrared laser and the ZGNR, we find that localized edge states mainly contribute to the generation of the low-order harmonics, while cutoff harmonics result from the other confined states. Our result shows that the edge-state effect of ZGNR with narrow width can enhance the conversion efficiency of low-order harmonics, rather than the higher-order harmonics extended to the cutoff region. High-order harmonic generation originated from zigzag graphene nanoribbons (ZGNRs) induced by intense laser pulses is investigated theoretically. During the interaction between the intense mid-infrared laser and the ZGNR, we find that localized edge states mainly contribute to the generation of the low-order harmonics, while cutoff harmonics result from the other confined states. Our result shows that the edge-state effect of ZGNR with narrow width can enhance the conversion efficiency of low-order harmonics, rather than the higher-order harmonics extended to the cutoff region.
Chinese Optics Letters
- Publication Date: Oct. 10, 2020
- Vol. 18, Issue 10, 103201 (2020)
All-fiber Yb:fiber frequency comb
Yawei Chang, Tongxiao Jiang, Zhigang Zhang, and Aimin Wang
We demonstrate an all-fiber Yb:fiber frequency comb with a nonlinear-amplifying-loop-mirror-based Yb:fiber laser oscillator. The fiber-spliced hollow-core photonic bandgap fiber was used as dispersion compensator, which was also directly spliced to a piece of tapered photonic crystal fiber for an octave-spanning spectrum. The spectrum of the compressed 107 fs laser pulses was broadened, covering 600 nm to 1300 nm in a high-nonlinearity tapered fiber for f to 2f beating. The signal-to-noise ratio of offset frequency was measured to be 22 dB. We demonstrate an all-fiber Yb:fiber frequency comb with a nonlinear-amplifying-loop-mirror-based Yb:fiber laser oscillator. The fiber-spliced hollow-core photonic bandgap fiber was used as dispersion compensator, which was also directly spliced to a piece of tapered photonic crystal fiber for an octave-spanning spectrum. The spectrum of the compressed 107 fs laser pulses was broadened, covering 600 nm to 1300 nm in a high-nonlinearity tapered fiber for f to 2f beating. The signal-to-noise ratio of offset frequency was measured to be 22 dB.
Chinese Optics Letters
- Publication Date: May. 10, 2019
- Vol. 17, Issue 5, 053201 (2019)
Intensity modulation of filaments by shaped laser pulses in fused silica
Junwei Chang, Ruihan Zhu, Tingting Xi, Mengning Xu, Di Wang, Lanzhi Zhang, Dongwei Li, and Zuoqiang Hao
We show the intensity control of filamentation in fused silica by temporally shaping the femtosecond laser pulse. The arbitrary control of filamentation intensity has been obtained by the feedback control based on the genetic algorithm, and the peak intensity of filament has changed from about 670 to around 2100 (charge-coupled device counts). This modulation is in qualitative agreement with the simulation results. It is shown that the control of the intensity is realized by modulating the peak power of the shaped pulse. We show the intensity control of filamentation in fused silica by temporally shaping the femtosecond laser pulse. The arbitrary control of filamentation intensity has been obtained by the feedback control based on the genetic algorithm, and the peak intensity of filament has changed from about 670 to around 2100 (charge-coupled device counts). This modulation is in qualitative agreement with the simulation results. It is shown that the control of the intensity is realized by modulating the peak power of the shaped pulse.
Chinese Optics Letters
- Publication Date: Dec. 10, 2019
- Vol. 17, Issue 12, 123201 (2019)
Generation of femtosecond dual pulses by a transverse standing wave in a volume holographic grating
Xiaoyan Wang, Xiaona Yan, Kailong Jin, Ye Dai, Zuanming Jin, Xihua Yang, and Guohong Ma
Based on Kogelnik’s coupled-wave theory, it is found that when a femtosecond pulse is incident on a transmitted volume holographic grating, two transverse standing waves along the grating vector direction will be generated inside the volume holographic grating (VHG). Due to field localization of two standing waves, they have two different velocities along the propagation depth. On the output plane of the VHG, femtosecond dual pulses are generated in both the diffracted and transmitted directions. Results show that the pulse interval is determined by the refractive index modulation and thickness of the grating, while the waveform of the dual pulses is independent of the grating parameters. Based on Kogelnik’s coupled-wave theory, it is found that when a femtosecond pulse is incident on a transmitted volume holographic grating, two transverse standing waves along the grating vector direction will be generated inside the volume holographic grating (VHG). Due to field localization of two standing waves, they have two different velocities along the propagation depth. On the output plane of the VHG, femtosecond dual pulses are generated in both the diffracted and transmitted directions. Results show that the pulse interval is determined by the refractive index modulation and thickness of the grating, while the waveform of the dual pulses is independent of the grating parameters.
Chinese Optics Letters
- Publication Date: Nov. 10, 2019
- Vol. 17, Issue 11, 113201 (2019)
Effect of metal surface morphology on nano-structured patterns induced by a femtosecond laser pulse and its experimental verification
Haiying Song, Shengwang Tan, Elshaimaa M. Emara, Yanjie Zhang, Shibing Liu, Yao Li, and Haiyun Liu
The effect of material surface morphology on the periodic subwavelength of nano-structures induced by a femtosecond (fs) laser was investigated systematically from the initial surface roughness, the different scratches, the pre-formed ripples, and the “layer-carving” technology experiments. The results of the comparative experiments indicate that the initial surface conditions of the target surface have no obvious effects on the spatial structured periods (SSPs) and the ripple orientation of the periodic nano-structures induced by a fs laser, which agreed well with the foretold present surface two-plasmon resonance (STPR) model. Furthermore, different shapes of nano-grids with high regularity and uniformity were obtained by fs-laser fabrication. The effect of material surface morphology on the periodic subwavelength of nano-structures induced by a femtosecond (fs) laser was investigated systematically from the initial surface roughness, the different scratches, the pre-formed ripples, and the “layer-carving” technology experiments. The results of the comparative experiments indicate that the initial surface conditions of the target surface have no obvious effects on the spatial structured periods (SSPs) and the ripple orientation of the periodic nano-structures induced by a fs laser, which agreed well with the foretold present surface two-plasmon resonance (STPR) model. Furthermore, different shapes of nano-grids with high regularity and uniformity were obtained by fs-laser fabrication.
Chinese Optics Letters
- Publication Date: Jul. 10, 2018
- Vol. 16, Issue 7, 073202 (2018)
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